A multilayer ceramic capacitor as an example of electronic devices is formed by printing a conductive paste on a green sheet made by a predetermined dielectric ceramic composition, stacking a plurality of the green sheets on which the conductive paste is printed, and integrally firing the green sheets and internal electrodes.
A conventional dielectric ceramic composition had a property of being reduced and becoming semiconductive when fired in a neutral or reducing atmosphere having a low oxygen partial pressure. Therefore, when producing a multilayer ceramic capacitor, it was inevitable to fire in an oxidizing atmosphere having a high oxygen partial pressure. Due to this, as an internal electrode material to be fired together with the dielectric ceramic composition, it has been required to use expensive precious metals (for example, palladium and platinum) which are not fused at a temperature the dielectric ceramic composition is sintered and not oxidized even when fired in an oxidizing atmosphere. It has been a big obstacle of realizing a low price of a multilayer ceramic capacitor to be produced.
To use inexpensive base metals (for example, nickel and copper) as a material of an internal electrode, it is necessary to develop a dielectric ceramic composition which does not become semiconductive even when fired in a neutral or reducing atmosphere, that is, has an excellent reducing resisting property and has a sufficient specific dielectric constant and excellent dielectric characteristics after firing (for example, having a small capacity-temperature change rate).
Conventionally, a variety of proposals have been made for dielectric ceramic compositions capable of using a base metal as a material of an internal electrode.
For example, the Japanese Unexamined Patent Publication No. 11-224827 discloses a dielectric ceramic composition composed of a main component made by a dielectric oxide having a composition expressed by (Ca1-xMex)m.(Zr1-yTiy)O3 (note that 0.90<m<1.10, 0.1≦x≦0.9, 0≦y≦0.5) and SiO2, B2O3, Mn2O3 and Ln2O3 (note that Ln is at least one or two kinds of elements selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), wherein a content ratio of SiO2+B2O3 in the dielectric ceramic composition is 0.1 to 5 wt %, a content ratio of Mn2O3 is 0.1 to 3.0 atomic % and a content ratio of Ln2O3 is 0.03 to 1.0 atomic %.
Also, the Japanese Unexamined Patent Publication No. 60-131708 discloses a dielectric ceramic composition composed of a main component made by a dielectric oxide having a composition expressed by (Ca1-xSrx)m.(Zr1-yTiy)O3 (note that 0.85<m<1.30, 0≦x<0.6, 0≦y<0.6) and zMnO2 (note that 0.005<z<0.08 in a weight ratio with respect to 1.00 of the main component).
Furthermore, the Japanese Examined Patent Publication No. 57-37081 discloses a dielectric ceramic composition composed of a main component made by a dielectric oxide having a composition expressed by (Ca1-xBax)m.ZrO3 (note that 0.85<m<1.30, 0<x<0.2) and zMnO2 (note that 0.005<z<0.08 in a weight ratio with respect to 1.00 of the main component).
Moreover, the Japanese Unexamined Patent Publication No. 63-126117 discloses a dielectric ceramic composition containing a dielectric oxide having a composition expressed by (Ca1-xSrx)m.(Zr1-yTiy)O3 (note that 0.85<m<1.30, 0≦x<0.6, 0≦y<0.6) as a main component and 0.5 to 8 parts by weight of MnO2 and 0.5 to 8 parts by weight of glass component (note that the glass component uses predetermined mole ratios of Li2O, RO (note that R is at least one kind selected from Ba, Sr, Ca and Mg), (Ti, Si)O2 and Al2O3) with respect to 100 parts by weight of the main component).
However, any of the dielectric ceramic compositions described in the above publications had disadvantages that dielectric characteristics (capacity change, dielectric loss) were deteriorated by a low frequency after firing, or an accelerated lifetime of insulation resistance was short, and reliability of an obtained multilayer ceramic capacitor became poor when producing a multilayer ceramic capacitor having an internal electrode made by a base metal, such as nickel, by using the dielectric ceramic composition.